On effective degrees of freedom at chiral restoration and the vector manifestation

Recent research activities on the chiral structure of hadronic matter near the phase transition predicted by QCD and extensively looked for in terrestrial laboratories as well as in satellite observatories raise the issue of whether we have fully identified the relevant degrees of freedom involved in the transition. In this talk, I would like to discuss a recent novel approach to the issue based on the 'vector manifestation' scenario discovered by Harada and Yamawaki in hidden local symmetry theory. For simplicity, I will restrict myself to two extreme scenarios: one that we shall refer to as 'standard' in which pions are considered to be the only low-lying degrees of freedom and the other that could be referred to as non-standard' in which in addition to pions, other degrees of freedom figure in the process. In particular, I shall consider the scenario that arises at one-loop order in chiral perturbation theory with hidden local symmetry Lagrangian consisting of pions as well as nearly massless vector mesons that figure importantly at the 'vector manifestation (VM)' fixed point. It will be shown that if the VM is realized in nature, the chiral phase structure of hadronic matter can be much richer than that in the standard one and the chiral phase transition will be a smooth crossover: Sharp vector and scalar excitations are expected in the vicinity of the critical point. Some indirect indications that lend support to the VM scenario are discussed. (author)